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I'm building a loft bed for a queen size bed. I planned to build a platform and support it with 4x4s, but I'm having trouble finding untreated 4x4s. I plan to loft the bed 5' or so. The platform will be made of 2x6's covered in 1/2" plywood.

This shows what I'm planning to do:

enter image description here

Can I use two 2x4s instead of the 4x4's to carry the load?

If so, will nailing/screwing them together in several places be sufficient to hold them together?

I'd like to use 3/8" bolts to join the platform to the posts (for easy disassembly). If so, should I only bolt down the long side of the platform, or try to place bolts on both sides of the corner? If the latter, how should I put a bolt through the narrow side of the joined boards?

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1 Answer

2 2x4s are not square, if that matters (3 x 3.5). They will be plenty strong as assembled posts.

Try a traditional lumber yard, they will have untreated pine. Cedar may also be an option.

Your structure would be better supported if you shortened 1 of the 2 paired 2x4s at each corner and made a jack-king stud arrangement like a door frame and header. The main tenant of construction is to bear the weight with structural components and only use fasteners to keep the structure in place, not to bear the load (in shear).

You are, in effect, making a small deck. You should attach the rear 2x8 2x6 to each wall stud. A 4" #10 decking screw would not be too small .

The front and rear members are, in effect, beams and should be 2x8s. The joists running perpendicular to the beam should be 2x6 2x4s hung with joist brackets.

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Yes it is a deck of sorts, but instead of a 60psf live load for a crowd of people dancing, for which your size recommendations are completely appropriate, we're looking at more like 15psf live load for 2 people, um... "dancing". 2x4 joists and 2x6 beam will be fine, IMO. Compare with the member sizes often seen in commercial bed frames. I feel like I'm nit-picking you with minor details, even though you always have excellent answers. I call 'em as I see 'em. –  bcworkz Apr 6 '13 at 21:03
    
I'd go for a bit of downsizing, if they did the jack/king, lagged one side and used hangers. Anyone mamboing up in the air may draw a crowd... –  HerrBag Apr 6 '13 at 21:10
    
Thanks for the help! Could you give some advice about how I should attach the posts to the platform? I'd like to use removable fasteners (e.g. bolts) so I can move the thing from time to time. I'm not sure how many and where is good to place them. I'm also not positive how I should attach the "jack" stud to the platform (without nails). The images below are what I think should work, but I'd love some input. Outside Inside –  bgt421 Apr 8 '13 at 2:32
    
Your jack is correct, forming a ledge for the beam (front and rear 2x6s) No beam to jack connector (toe nails or such) are needed. The king to jack connections (a pair of screws every 12") will solidify the beam. I would spread your upper and lower face bolts (beam to king) on either side of the king center line.. 1" either side of centerline. If you use carriage bolts, be sure to use washers on the inside.. Pine is quite soft and they will bury. I would use deck screws in place of nails.. 3" for framing connections. Screw down your plywood into all beams and joist. –  HerrBag Apr 8 '13 at 3:39
    
I would use construction adhesive at all plywood to structure contact. (I favor polyurethane adhesive) –  HerrBag Apr 8 '13 at 3:41
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